Night vision systems are used in a wide variety of military, industrial and residential applications to enable sight in a dark environment. For example, night vision systems are utilized by military aviators during nighttime flights or military soldiers patrolling the ground. Security cameras use night vision systems to monitor dark areas and medical instruments use night vision systems to alleviate conditions such as retinitis pigmentosis (night blindness).
Conventional image enhancement night vision equipment utilize an Image Intensifier (I2) to amplify an image. The image intensifier collects tiny amounts of light in a dark environment, including the lower portion of the infrared light spectrum, that are present in the environment but may be imperceptible to the human eye. The image intensifier amplifies the light so that the human eye can perceive the image. The light output from the image intensifier can either be supplied to a camera, external monitor or directly to the eyes of a viewer. The image intensifier devices are commonly employed in goggles, i.e. a monocular or binocular, that are worn on a user's head for transmission of the light output directly to the viewer.
Image enhancement night vision equipment utilizes available light such as starlight and moon light. Although the image enhancement equipment will work in very reduced lighting, it may not work as well in environments of absolute darkness, such as caves or caverns. Furthermore, image enhancement equipment effectiveness may be reduced by battlefield obscuration such as smoke, fog, rain, dust, and foliage. For those reasons, standard night vision devices may be enhanced with the addition of thermal imaging, i.e. infrared (IR) information.
Whereas conventional night vision devices employing image intensifiers can only see visible wavelengths of radiation, the enhanced system provides additional situational awareness by providing infrared (i.e. heat) information to the image. A typical scenario where this might be important is where a camouflaged person cannot be seen with an image intensifier device. However, with the addition of infrared information to the same image, the camouflaged person's heat signature is visible.
The enhanced night vision device commonly includes two channels, each channel including an image detector for transmitting a scene image to the user. The first channel includes a thermal camera (i.e., an infrared detector), for example, and a complementary objective lens to transmit a scene image in a first spectral band. The second channel includes an image intensifier camera, for example, and a complementary objective lens to transmit the same scene image in a second spectral band. A processing module within the night vision device fuses the images together and superimposes the images on each other. Such a device is disclosed in U.S. Pat. No. 6,560,029 which is incorporated herein by reference in its entirety.
To change the focus of each channel of the enhanced night vision, the end user adjusts the relative distance between an image detector and its complimentary objective lens. U.S. Pat. No. 7,116,491 to Willey et al., which is incorporated by reference herein, discloses a focusing mechanism that is configured to simultaneously adjust focus of two optical channels by simultaneously translating both image detectors relative to their respective objective lenses.
In various night vision devices, such as that described in U.S. Pat. No. 7,116,491 (the '491 patent), each image detector moves relative to its complementary objective lens, or vice versa. In a common arrangement, a bore that forms part of an image detector translates over an exterior revolved surface of a cylinder that forms part of a complimentary objective lens, or vice versa. The amount of clearance between the cylinder and the bore is dictated by the accuracy of the machines that form the bore and the cylinder. The amount of clearance between the cylinder and the bore is tailored such that the cylinder can freely slide within the complimentary bore, while ‘play,’ i.e., clearance, between the cylinder and the bore is limited. In multi-channeled systems, excessive play between the bore and the cylinder may be detrimental because the play may manifest itself as error between overlaid images (i.e., pixel matching). Maintaining a tight tolerance to limit excessive play while permitting the bore to freely slide over the cylinder is a relatively expensive proposition. There exists a need to improve upon the focus mechanism of a multi-channel optical system in the interest of cost, manufacturability and performance.
Various multi-channel night vision devices, such as that described in the '491 patent, do not include provisions for adjusting the relative focus of the channels, i.e., the focus of one channel with respect to the focus of another channel. In the '491 patent, the focus of both channels is adjusted simultaneously by rotating a single knob. It is not possible to adjust the focus of one channel independently of the focus of another channel without disassembling the night vision device. It would be beneficial to include provisions for adjusting the relative focus of each channel without disassembling the night vision device in the interest of usability.